The present invention relates to load compensating bearings and a roller load measuring device. In another aspect the invention relates to an improved method and device for measuring applied load to roller circle construction for a machine having upper and lower frames rotatable with respect to each other in which peak roller loads cause structural and bearing failures. In yet another aspect, the invention is particularly suitable for monitoring bearing loads placed on very large earth moving machinery through in use measurement of rolling element bearing loads.
Heavy earth moving equipment such as draglines, cranes, power shovels and the like generally are supported on a stationary lower portion with the upper portion being rotatable with respect to the lower portion. The upper portion or frame is pivotably supported on a lower portion frame by a live roller circle. In order for the rotatable movement to occur, a vertical center pin is provided with a surrounding circular bearing track or circle having an upper bearing rail attached to the upper frame, a lower bearing rail attached to the lower frame in juxtaposed relationship with the upper bearing rail, and a roller bearing circle having a plurality of conical roller bearings therein for supporting the upper and lower bearing rail. The rollers transmit the weight of the upper frame section and the load handled thereby to the roller bearing circle and, thus, to the lower frame section which is generally stationary. In machines of large size, the load transmitted through the rollers to the lower frame are paramount and can amount to several million pounds. In those machines utilizing a load handling boom which is pivotally connected to the front edge of the rotating frame, the heaviest loads are transmitted to the roller circle bearings in the region of the front edge of the rotating frame or, when the frame is rotated with the load, the heaviest load is transferred to the rolling elements sequentially around the circle.
The application of nonuniform and highly concentrated loads of these magnitudes on small segments of the bearing roller circle create extremely high stresses developed by such loads causing roller bearing deterioration and eventual failure. These highly concentrated loaded conditions create premature wear and failure of the rails and roller bearings which is a costly matter. The large costly machine must be taken out of service with down time sometimes being more costly than the cost of damage to parts and costly materials. The live roller circle consisting of a circular upper rail attached to the underside of the upper frame resting on a complete circle of rollers which, in turn, rests upon a circular lower rail mounted upon the top of the lower frame or base is called "live" in order to distinguish it from slewing rings or other arrangements in common use in which bearing rollers are mounted on shafts affixed to the upper frame. Although live roller circles are generally regarded as the most suitable rotary support for large excavators, they are not without problems.
A frequent problem is the excessive and permanent failure of the rollers due to overloading, uneven surfaces, etc.
Attempts have been made to ascertain the loads which may be transmitted by the live roller circle and rolling elements. However, such attempts have included taking strain readings at selected positions of the structure and from these readings inferring the load transmitted through the bearings. Many factors are assumed in the calculation in the inferred maximum load on any one load bearing element and, thus, the load which is calculated to be transmitted by a particular roller bearing element may be inaccurate. Other methods have included apparatus for measuring roller element bearing loads by the presentation of apparatus for measuring and recording instantaneous bearing loads or the loads on individual components. As it is not possible to build these roller bearing assemblies on raceways which will not distort in hearty loaded use, the roller retaining shafts are loosely fit in the bore of the rollers to enable the rollers to float with respect to the cage to accommodate the distortion of the raceway. In other adaptations the pins are closely fit into the bore of each roller wherein flexible cage distortion is allowed to enable the rollers to conform to the raceway distortion to maximize load sharing.
Methods have been presented wherein the working load of each roller can be monitored by arranging engaging apparatus in the roller element cavity. Measuring apparatus for determining load applied to rolling elements including sensing means have been adapted to be supported in the cavity of the rolling element to monitor a dimension of the cavity which varies with variation as load is applied to said bearing assembly and communication means associated with said sensing means in such a manner as to provide said monitored dimension. Such teachings as found in U.S. Pat. No. 4,175,430 provide a load measuring device inclusive of a measuring device consisting of either a telescope engaging assembly or a transducer assembly mounted inside the roller element bore and within an aperture of a roller retaining shaft configuration. The patent teaches a sensing means for monitoring at least one dimension of the cavity which varies with variations in the load applied.
Need still exists for measurement of applied loads to these roller bearing assemblies which provide the combined effect of three-dimensional change. Significant advantages to measuring volumetric change, as opposed to measuring a single dimension change, are readily understood since the measurement of volume involves almost the entire length of the roller and acts as an averaging device that averages loading effects that are not necessarily evenly distributed along the length of the roller. Volumetric measurements are less likely to be affected by an out-of-round roller bore than, for example, a measuring device which only measures the bore diameter.
Therefore, it is an object of the present invention to provide a three-dimensional method and device for determining rolling element bearing loads. This object is achieved in a rolling element bearing assembly by replacement of the normal roller retaining shaft with a sealing, rotating device allowing the cavity of the rolling element to be filled with fluid. When load is applied to the rolling element, a measurable corresponding volume change occurs which is correlatable to actual load.